In American football, blocking or interference (or running interference) involves legal movements in which one player uses his body to obstruct another player's path. The purpose of blocking is to prevent defensive players from tackling the ball carrier, or to protect a quarterback who is attempting to pass, hand off or run the ball. Offensive linemen and fullbacks tend to do the most blocking, although wide receivers are often asked to help block on running plays and halfbacks may be asked to help block on passing plays, while tight ends perform pass blocking and run blocking if they are not running routes to receive passes. Overall, blocking is a skill that virtually every football player may be required to do at some point, even defensive players in the event of a turnover.

Essentially, blocking is pushing, with certain restrictions; in blocking one may not grasp another player or do any sort of pulling, and the hands must not extend beyond the line of each armpit; otherwise a holding penalty will be assessed. Blocking is also not permitted beyond five yards from the line of scrimmage until the quarterback has handed off the ball to a runner or a receiver has touched the ball after it has been passed.

Outside sports, "running interference" is a metaphor that refers to a person's helping someone in the performance of a task without directly assisting in the task. Often this is done by attracting attention to oneself (so as to deflect attention from the other person) or throwing oneself into harm's way.